1. Field of the Invention
The present invention relates particularly to an intake duct device that leads traveling air taken from a front surface of a cowling to an air cleaner in a motorcycle.
2. Description of the Related Art
The layout for leading intake air to an engine through the vicinity of a steering head pipe is an excellent structure in view of intake efficiency, layout efficiency of parts, and so on. As a structure of this type that passes outside air led from a front side of a body frame through an air passage that is penetratingly provided at a front portion of a body frame, one disclosed in Patent Document 1 has been known. In the structure in Patent Document 1, a member of a frame main body itself of the body frame penetrates through a steering head pipe part and is fastened to an intake duct in front thereof.
Here, since vehicles traveling on public roads generally have a large steering angle and a narrow fork pitch of a front fork, their intake ducts have a small sectional area. On the other hand, since racing vehicles and the like have a small steering angle and a wide fork pitch of a front fork, their intake ducts can have a large sectional area.
Patent Document 1: Japanese Laid-open Patent Publication No. 2007-196984
In the conventional intake duct structure in which the intake duct penetrating through the steering head pipe part is formed in the body frame itself, the sectional area of the intake duct is fixed, that is, the sectional area of the intake duct cannot be changed unless the frame main body is changed. As a typical example, it is practically impossible to cope with a requirement in such cases as when a vehicle traveling on public roads being a mass-produced vehicle is converted to a racing vehicle.